x1.trial = rnorm(443)
x2.trial = .5*rnorm(443)+3
y.trial = .4*x1.trial+.2*x2.trial + .5*rnorm(443)

dataset = as.data.frame(cbind(y.trial,x1.trial,x2.trial))

crossval1 = cv.lm(df=dataset ,seed=5000, form.lm=formula(y.trial ~ x2.trial + x2.trial))
crossval2 = cv.lm(df=dataset ,seed=5000, form.lm=formula(y.trial ~ x2.trial + x1.trial))

form.lm=ols.regression1
df=dataframe